JP 10-132614 A describes an optical encoder that can obtain a displacement signal without causing a position detection error and with little distortion, even if tarnishing or scratching of a scale occurs, by arranging light receiving elements if a plurality of different groups for every phase.
If it is possible to make the light receiving region of the light receiving elements narrow, it is easy to simplify a light source, making it possible to reduce the cost of the optical encoder. With an arrangement method for light receiving elements disclosed in an embodiment of the optical encoder disclosed in JP 10-132614 A, a gap between light receiving elements is still wide. As a result, there has been a need for an optical encoder that can obtain a displacement signal with which no position detection error occurs and with little distortion, even if tarnishing or scratching of the scale occurs, particularly one operating with a much narrower gap between light receiving elements. Also, the wider the gap between light receiving elements the more ineffective light increased, and wasted power consumed by the light source increased in proportion to this ineffective light. As a result, there has also been a need for an encoder with narrow gaps between light receiving elements from the viewpoint of energy conservation.
The present invention has been conceived in view of the above-described situation, and an object of the present invention is to provide a high precision optical encoder by devising an arrangement method for optical elements that can obtain a displacement signal with which no position detection error occurs and that has little distortion, even if a scale becomes tarnished or scratched, and by enabling operation with narrow light receiving regions, to thereby realize cost reduction and reduced power consumption by simplifying a light source.